Illumination device utilizing displaced radiation patterns

ABSTRACT

In one embodiment, the invention is directed to an illumination device. The illumination device includes a light emitting diode that emits a radiation pattern, wherein a maximum luminous intensity of the radiation pattern is displaced relative to a center axis of the light emitting diode. The illumination device may also include a number of light guides positioned to be illuminated by the light emitting diode. The invention utilizes the “batwing” radiation pattern of a light emitting diode to effectively illuminate a number of light guides with a single light emitting diode. Each light guide is offset from a center axis of the light emitting diode to capture light that is annularly displaced. This offset positioning of the light guides allows the light guides to effectively capture light from the light emitting diode where light intensity is greatest.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/918,262, filed Jul. 30, 2001, the entire content of which isincorporated herein by reference.

FIELD

The invention relates to light guides for functional or decorativelighting and light sources having radiation patterns in which themaximum luminous intensity is displaced.

BACKGROUND

Light guides can be used to provide functional or decorative lighting.Functional lighting refers to lighting that is used for the purpose ofilluminating an object or area to make the object or area moreconspicuous. Decorative lighting refers to lighting that is used foraesthetic purposes. Often, light guides are used for both functional anddecorative purposes.

A light source can be used to illuminate one or more light guides suchthat light is transmitted through the light guides via total internalreflection. Light guides may provide side lighting, in which light isemitted from the sides of the guides. In addition, light guides mayprovide end lighting, in which light is emitted from the end of theguides. A variety of different extraction techniques using notches orcoating, for example, can be applied to the light guides to cause lightto be emitted from the light guides in a controlled or random manner.

Lighting systems that implement light guides generally have a lightsource that illuminates the light guide. For example, incandescent lightsources, florescent light sources, or light emitting diodes are oftenused to illuminate a light guide. The light source may reside in a lightsource assembly, also referred to as an illuminator. The light can betransmitted down the light guide, possibly changing colors or pulsatingover time to provide the desired functional or decorative effect.

Light emitting diodes are particularly well suited for illuminatinglight guides because light emitting diodes are point-like light sources.Moreover, light emitting diodes use less energy than many other lightsource alternatives. Some light emitting diodes, however, have “batwing”radiation patterns in which the maximum luminous intensity of the lightemitting diodes is angularly displaced. Therefore, conventional lightingsystems that utilize light emitting diodes often utilize correctiveoptics to correct for the angular displacement of the radiation patternand provide peak radiation intensity along a center axis of the lightemitting diodes.

SUMMARY

The invention utilizes the “batwing” radiation pattern of a lightemitting diode to effectively illuminate a number of light guides with asingle light emitting diode. Each light guide is offset from a centeraxis of the light emitting diode to capture light that is annularlydisplaced. This offset positioning of the light guides allows the lightguides to effectively capture light from the light emitting diode wherelight intensity is greatest.

In one embodiment, an illumination device includes a light emittingdiode that emits a radiation pattern, wherein a maximum luminousintensity of the radiation pattern is displaced relative to a centeraxis of the light emitting diode. The illumination device may alsoinclude a number of light guides positioned to be illuminated by thelight emitting diode. Each light guide can be positioned at offsetlocations relative to the center axis of the light emitting diode. Forexample, each light guide may be positioned such that a cross-sectionalcenter of each light guide substantially corresponds to locations of themaximum luminous intensity of the radiation pattern of the lightemitting diode. In this manner, a single light emitting diode can beused to illuminate a number of light guides in an effective manner.

The illumination device may also include a light guide fixture formed tomate with the light guides. The light guide fixture can be used toposition the light guides at the offset locations relative to the centeraxis of the light emitting diode. For example, the light guide fixturemay be positioned adjacent the light emitting diode and the light guidesmay be mated with the light guide fixture. In this manner, each lightguide can be positioned such that a cross-sectional center of each lightguide substantially corresponds to a location of the maximum luminousintensity of the radiation pattern of the light emitting diode. In someembodiments, the light guide fixture forms a housing that houses thelight emitting diode.

In another embodiment, the invention is directed toward a sign. The signmay include a frame, and a light emitting diode that emits a radiationpattern, wherein a maximum luminous intensity of the radiation patternis displaced relative to a center axis of the light emitting diode. Thelight emitting diode may be housed within the frame. The sign may alsoinclude a number of light guides positioned to be illuminated by thelight emitting diode, and each light guide can be positioned at anoffset location relative to the center axis of the light emitting diode.The frame can be formed with holes and each light guide may protrudethrough at least one of the holes.

In still another embodiment, the invention is directed toward a method.The method may include positioning a number of light guides next to alight emitting diode that emits a radiation pattern, wherein a maximumluminous intensity of the radiation pattern is displaced relative to acenter axis of the light emitting diode. Each light guide can bepositioned at an offset location relative to the center axis of thelight emitting diode. The method may also include illuminating the lightguides with the light emitting diode. In this manner, the light emittingdiode can be used to effectively and efficiently illuminate a number oflight guides.

The invention is capable of providing several advantages. For example,the use of light emitting diodes as opposed to other light sources canreduce power consumption. Moreover, light emitting diodes can be morereliable than other light source alternatives. In addition, lightemitting diodes generally have longer lifespans than other light sourcealternatives. Power can also be saved by illuminating a number of lightguides with a single light emitting diode according to the invention.

The invention can also produce more uniform lighting in the number oflight guides that are illuminated by the same light emitting diode.Intensity variation between different light emitting diodes can berelatively large. Indeed, some light emitting diodes are sold at highercosts when the amount of acceptable variation in light output betweendifferent light emitting diodes is minimized. The invention, however,can utilize the same light emitting diode to illuminate a number oflight guides in a substantially uniform manner. Thus, even therelatively lower cost light emitting diodes can be used to illuminatemultiple light guides in a substantially uniform manner.

Another advantage of the invention is the avoidance of correctiveoptics. As mentioned above, conventional teaching has viewed angulardisplacement of peak radiation intensity as a problem requiring the useof corrective optics. The invention, however, utilizes and exploitsangular displacement of peak radiation intensity as a benefit thatimproves the way in which a number of light guides are illuminated bythe same light emitting diode. In this manner, the invention can provideboth an improved lighting system, and also a lighting system havingfewer optical elements than conventional systems that utilize correctiveoptics to compensate for the angular displacement of peak radiationintensity.

Still another advantage can be realized by using light guides thatprovide directional side lighting. Each of the light guides that areilluminated by the single light emitting diode can direct light indifferent directions. This can be especially advantageous for use withsigns that are positioned for viewing by persons close to the sign andother persons far away from the sign. The use of a single light emittingdiode to illuminate two light guides can ensure that the light guidesare illuminated substantially uniformly. The two different light guidesmay provide directional lighting in different directions. If used in asign, for example, the first light guide may direct light downward,toward persons close to the sign, and the second light guide may directlight outward, toward persons a significant distance from the sign.

Additional details of these and other embodiments are set forth in theaccompanying drawings and the description below. Other features, objectsand advantages will become apparent from the description and drawings,and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective exploded view of an illumination deviceaccording to the invention.

FIG. 2 is a side-view of an illumination device as shown in FIG. 1.

FIG. 3 is a graph illustrating a typical “batwing” radiation pattern ofa light emitting diode that can be used in accordance with theinvention.

FIG. 4 can be viewed as either a side view or a top view of light guidespositioned relative to a light emitting diode.

FIGS. 5-8 are cross-sectional views illustrating embodiments wherein thelight guides are positioned along the peak luminous intensity angle of alight emitting diode.

FIG. 9 is a top perspective view of light guides illuminated by lightemitting diodes on both ends.

FIG. 10 is a perspective view illustrating an example sign according tothe invention.

DETAILED DESCRIPTION

In general, the invention provides an illumination device for providingeffective and efficient lighting. The illumination device can beimplemented in any number of different applications to provide uniformlighting via a number of light guides illuminated by the same lightemitting diode. The invention utilizes the “batwing” radiation patternof the light emitting diode to facilitate and improve illumination ofthe number of light guides. Each light guide is offset from a centeraxis of the light emitting diode to capture light that is angularlydisplaced. This offset positioning of the light guides allows the lightguides to effectively capture light from the light emitting diode wherelight intensity may be greatest. In one particular application, theinvention is implemented in a sign. However, the invention could be usedin any application where lighting is desirable.

FIG. 1 is a perspective exploded view of an illumination device 10according to the invention. FIG. 2 is a side view of the assembledillumination device 10. Illumination device 10 includes a light emittingdiode 12 and a number of light guides. A first light guide 14 and asecond light guide 16 are shown for illustrative purposes. However, anynumber of light guides could be used according to the invention. Indeed,even a single light guide could be used. Suitable light guides, forexample, as described in U.S. Pat. No. 5,845,038 are commerciallyavailable from Minnesota Mining and Manufacturing Company of St. Paul,Minn. Other light guides could also be used, including light guideshaving any particular cross-sectional shape. For example, light guideshaving cross-sectional shapes that are square, rectangular, polygonal,circular, or any other shape could be used in accordance with theinvention.

Illumination device 10 may also include a light guide fixture 18 formedwith holes 20, 22 for mating with light guides 14 and 16. For example,light guide fixture 18 can be used to properly position light guides 14and 16 relative to light emitting diode 12. Illumination device 10 mayalso include heat sink 24 to dissipate heat away from light emittingdiode 12, and a connector 26 coupled to light emitting diode 12. Forexample, connector 26 may be used to connect light emitting diode 12 toa power supply (not shown). Light emitting diode 12 may reside on plate13, although the invention is not limited in that respect.

Light emitting diode 12 is a light emitting diode having a “batwing”radiation pattern, in which the maximum luminous intensity of the lightemitting diode is angularly displaced. Luminous intensity refers to theflux density of light emitted from light emitting diode 12 at a positionin space. The radiation pattern of a light emitting diode describes howthe flux is distributed in space. The radiation pattern can be describedby defining the intensity of the light emitting diode as a function ofangle from the center axis of the light emitting diode, i.e., an opticalaxis extending outward from the center of the light emitting diode. Asuitable light emitting diode, for example, is the Luxeon™ Star/Cavailable from LumiLeds of San Jose, Calif.

FIG. 3 is a graph illustrating a typical “batwing” radiation pattern ofa light emitting diode that can be used in accordance with theinvention. The graph shows the relative luminous intensity as a functionof angular displacement. The graph also illustrates where the term“batwing” radiation pattern comes from, i.e. the shape of the curveresembles batwings. Consequently, the maximum luminous intensity oflight emitted from light emitting diode 12 occurs at locations that areoffset from the center axis. In other words, as shown in FIG. 3, thepeaks that define the maximum luminous intensity occur at a definedangle relative to the center axis. Depending on the particular lightemitting diode, the maximum luminous intensity may occur at differentangles. In FIG. 3, the maximum luminous intensity occurs atapproximately 40 degrees from the center axis. In general, the anglethat defines the maximum luminous intensity is referred to herein as thepeak luminous intensity angle.

In many of the exemplary embodiments described below, the maximumluminous intensity angle is assumed to be substantially rotationallysymmetric around the center axis of the light emitting diode. However,the invention may also be implemented with light emitting diodes havingnon-symmetric maximum luminous intensity angles. For example, lightemitting diodes may have a number of different maximum luminousintensity angles, or the maximum luminous intensity angle may bedifferent in different directions. In general, however, the invention ismost effective for use with light emitting diodes having at least onelocal maximum intensity angle that is off center.

If the maximum luminous intensity angle is rotationally symmetric aroundthe center axis of the light emitting diode, the angular displacement ofthe maximum luminous intensity can be described as three dimensionallysymmetric. In other words, for a light emitting diode like that graphedin FIG. 3, the maximum luminous intensity may occur at every locationthat is 40 degrees from the center axis. Thus, a three dimensional graphof the maximum luminous intensity angle would appear cone-shaped. Ofcourse, as you move further away from the light emitting diode, the peakintensity also decreases. The maximum luminous intensity along any planeparallel to the light emitting diode graphed in FIG. 3, however, alwaysoccurs at approximately 40 degrees from center.

Angularly displaced maximum luminous intensity is conventionallyregarded as a problem. Often, corrective optics are used to correct forthis perceived problem. The corrective optics typically redistribute thelight to produce a radiation pattern that has a peak at or near thecenter axis.

In accordance with the invention, however, the “batwing” radiationpattern or angularly displaced maximum luminous intensity is utilizedand exploited to provide advantages for an illumination device. Inparticular, the illumination device may have a simpler construction thanmore conventional illumination devices. For example, one or more lightguides may be positioned such that the cross-sectional centers of thelight guides are positioned substantially along the peak luminousintensity angle. This construction can allow the light guides toeffectively capture as much light as possible without the use ofcorrective optics.

Referring again to FIGS. 1 and 2, light guide fixture 18 can be used toposition light guides 14, 16 such that the cross-sectional centers ofthe light guides are positioned substantially along the peak luminousintensity angle. Light guide fixture 18, for example, can be a machinedpiece of metal or a formed piece of plastic. Light guide fixture 18 mayform an illuminator housing for enclosure of light emitting diode 12, oralternatively, may simply be positioned adjacent light emitting diode 12to provide an interface between light guides 14, 16 and the emissionside of the light emitting diode. Alternatively, rather than light guidefixture 18, a suitable spacer, clamp, or the like may be used toproperly position light guides 14, 16 relative to light emitting diode12. Importantly, however, the positioning of light guides 14, 16 is atoffset locations relative to the center axis of light emitting diode 12so as to take advantage of the peak luminous intensity angle of lightemitting diode 12.

FIG. 4 can be viewed as either a side view or a top view of light guidespositioned relative to a light emitting diode. As shown, the positioningof light guides 14, 16 is at offset locations relative to the centeraxis 42 of light emitting diode 12. As can be appreciated by FIG. 4, iflight guides 14, 16 are positioned further away from light emittingdiode 12, the distance of the centers of the light guides to the centeraxis 42 increases. In general, the optimal positioning of the lightguides, when taking into account only the peak luminous intensity angle,can be defined as:X=Y tan(Φ),X defines the distance of the center of the light guide to the centeraxis 42 of the light emitting diode 12, Y defines the distance from theeffective point source within light emitting diode 12 to a plane definedby the cross-sectional side of the light guide into which light is to betransmitted, and Φ defines the peak luminous intensity angle. Of course,some slight amount of variation can be tolerated. For example, thecross-sectional centers may deviate slightly from the peak luminousintensity angle, but that would also result in reduced couplingefficiency.

Referring again to FIG. 4, in one embodiment, light guides 14, 16 havecross-sectional diameters of approximately 7 millimeters. Thus, if lightguides 14, 16 are placed directly beside one another such that the sideof the light guides follow the center axis 42 of light emitting diode12, and the peak luminous angle Φ=40 degrees, then the optimalpositioning of light guides 14, 16 taking into account only the peakluminous intensity angle Φ would be a distance Y=X/tan(Φ) away from theeffective point source within light emitting diode 12. In other wordsY=3.5/tan(Φ)=4.17 millimeters.

However, as light guides are positioned larger distances from the lightemitting diode, the flux into any given light guide also decreases, evenif the light guide is properly positioned along the peak luminousintensity angle. Thus, actual optimal performance may be achieved byboth minimizing the distance Y and positioning the center of the lightguides along the peak luminous intensity angle Φ. In some cases, optimalperformance can be achieved by reducing the distance Y at the expense ofoptimal positioning of the centers of the light guides along the peakluminous intensity angle Φ. In other words, it may be desirable toposition the light guides closer to the light emitting diode even ifdoing so causes the centers of the light guides to deviate from the peakluminous intensity angle Φ. For example, if the light guides haverelatively large diameters, positioning them more closely to the lightemitting diode may cause the cross-sectional centers of the light guidesto deviate from the peak luminous intensity angle. This is acceptable,of course, if it causes more light to be captured by the light guides.

Any number of light guides may be positioned along the peak luminousintensity angle, or more generally, at offset locations relative to thecenter axis of the light emitting diode in accordance with theinvention. FIGS. 5-8 are cross-sectional views illustrating embodimentswherein the light guides are positioned along the peak luminousintensity angle (indicated by the dotted line). FIG. 5 illustrates twolight guides, FIG. 6 illustrates three light guides, FIG. 7 illustratesfour light guides, and FIG. 8 illustrates eight light guides. As shown,the cross sectional centers of the light guides correspond to the peakluminous intensity angle. As described above, optimal performance mayactually be achieved by minimizing the distance of the light guides fromthe light emitting diode. In any case, however, the light guides arepositioned at offset locations relative to the center axis of the lightemitting diode. Many other configurations are also contemplated,including configurations having any number of light guides, andconfigurations in which the light guides are not positionedsymmetrically around a peak luminous intensity angle. For example, inFIG. 5, the light guides are illustrated as being on opposite sides ofthe center axis, but could alternatively be individually positioned atany offset location relative to the center axis of the light emittingdiode. In addition, light guides having various differentcross-sectional diameters could be positioned at offset locationsrelative to a center axis of the same light emitting diode.

FIG. 9 is a top perspective view of light guides illuminated by lightemitting diodes on both ends. Illumination device 90 includes a firstlight emitting diode, a second light emitting diode, and a number oflight guides 14, 16. For example, the light emitting diodes may resideon first and second plates 13A, 13B, although the invention is notlimited in that respect. Each of the number of light guides 14, 16 hastwo ends, and each end of each of the number of light guides ispositioned at offset locations relative to the center axis of one of thelight emitting diodes. Again, although illustrated as including twolight guides 14, 16, an illumination device according to the inventionmay include any number of light guides positioned at offset locationsrelative to the center axis of the light emitting diodes.

Illumination device 90 may also include first and second heat sinks 24A,24B to dissipate heat away from the first and second light emittingdiodes. In addition, illumination device 90 may include first and secondconnectors 26A, 26B coupled respectively to the first and second lightemitting diodes. For example, first and second connectors 26A, 26B maybe used to connect the light emitting diodes to one or more powersupplies (not shown).

First and second light guide fixtures 18A, 18B may be used to properlyposition the ends of light guides 14, 16 relative to the light emittingdiodes. For example, light guide fixtures 18A, 18B can be formed withholes for mating with each respective end of light guides 14, 16. Usinglight guide fixtures 18A, 18B, the respective ends of light guides 14,16 can be positioned relative to the light emitting diodes at offsetlocations relative to a center axis of the light emitting diodes. Inthis manner, illumination device 90 can take advantage of the batwingradiation patterns of the light emitting diodes.

Because illumination device 90 utilizes a light emitting diode at eachend of light guides 14, 16, the light guides may be illuminated withgreater intensity. In many cases, this can improve the visual effect.Importantly, however, the end of each light guide is positioned at anoffset location relative to a center axis of the respective lightemitting diode so that an angularly displaced peak of the radiationpattern of each light emitting diode is captured by each of the lightguides.

The use of light emitting diodes according to the invention providesadvantages over other light sources. In particular, light emittingdiodes may be generally better suited for illumination of light guidesthan other non-point like light sources. In addition, the use of lightemitting diodes as opposed to filament light sources, incandescent lightsources, or other light sources can reduce power consumption. Moreover,light emitting diodes can be more reliable than other light sourcealternatives, and may have longer lifespans that other light sourcealternatives.

The invention may also provide advantages by illuminating a number oflight guides with a light emitting diode. The invention may avoid theuse of costly connectors or splitters often used in more conventionallight guide bundles. Indeed, the need to bundle light guides to providelighting via a single illuminator can be avoided altogether. Rather,each of a number of light guides may be individually positioned relativeto a light emitting diode using a simple light guide fixture formed tomate with the light guides in a manner that properly positions the lightguides.

The invention can also produce more uniform lighting by illuminating anumber of light guides with the same illuminator or illuminators.Intensity variation between different light emitting diodes can berelatively large. Indeed, some light emitting diodes are sold at highercosts when the amount of acceptable variation in light output betweendifferent light emitting diodes is minimized. The invention, however,can utilize the same light emitting diode(s) to illuminate a number oflight guides in a substantially uniform manner. Thus, even therelatively lower cost light emitting diodes can be used to illuminatemultiple light guides substantially uniformly.

The invention may also avoid the use of corrective optics. Becauseconventional teaching has viewed angular displacement of peak radiationintensity as a problem, corrective optics have been developed to fixthis perceived problem. These corrective optics typically redistributethe light of an angularly displaced radiation pattern to provide aradiation pattern that has a peak at or near the center axis of thelight emitting diode. Because the invention effectively utilizes theangularly displaced radiation pattern, however, the invention may avoidthe need for corrective optics.

The invention can be used wherever lighting is desirable. One particularexemplary application of the invention is in a sign. FIG. 10 illustratesone example sign 100. Sign 100 utilizes illumination device 90 asillustrated in FIG. 9. For example, sign 100 may be formed with holes102A, 102B through which light guides 14, 16 protrude. The lightemitting diodes residing on plates 13A, 13B (FIG. 9), the light guidefixtures. 18A, 18B, the first and second heat sinks 24A, 24B, and thefirst and second connectors 26A, 26B may be housed within frame 104 ofsign 100. Some embodiments may utilize a number of illuminator deviceslike illumination device 90 of FIG. 9. For example, a sign may utilize anumber of illuminator devices, each having a pair of light guides likelight guides 14, 16.

Light guides 14, 16 may include notches, coating, or the like to providedirectional side lighting. In some embodiments, light guide 14 candirect light in a different direction than light guide 16. In otherwords, the two different light guides may provide directional lightingin different directions. For example, light guide 16 may direct lightdownward, toward persons close to sign 100, and light guide 14 maydirect light outward, toward persons a significant distance from sign100. This can be particularly useful for signs used in retail storecheckout lanes. For example, light guide 16 may need to be moreconspicuous to persons close to the sign, such as customers wonderingwhether the particular checkout lane associated with sign 100 is open.Light guide 14 may need to be more conspicuous to persons far away fromthe sign, such as managers needing to be notified of a problem in thecheckout lane associated with sign 100. In still other embodiments, thefirst light guide and the second light guide may provide differentcolors of light, e.g., via the use of one or more filters or differentfiltering material within the respective light guides or coated on therespective light guides. Alternatively, if more than one illuminationdevice having a pair of light guides is used, the different illuminationdevices may provide lighting with different colors.

In accordance with the invention, light guides can be properlypositioned and then illuminated. Properly positioning the light guidesaccording to the invention can improve the visual effect. For example,as described above, the light guides can be positioned at offsetlocations relative to a center axis of a light emitting diode so thatthe light guides capture angularly displaced light at or near the peakluminous intensity angle. In one embodiment, the light guides arepositioned such that the cross-sectional centers of the light guidessubstantially correspond to locations of the maximum luminous intensityof the radiation pattern of the light emitting diode. In otherembodiments, however, the distance of the light guides to the lightemitting diode is substantially minimized. In that case, thecross-sectional centers of the light guides may deviate slightly fromthe location of the maximum luminous intensity of the radiation patternof the light emitting diode. Importantly, however, the light guides arepositioned at offset locations relative to the center axis of the lightemitting diode. This can ensure that the light guides capture as muchlight as possible, which can in turn enhance the visual effect.

Many implementations and embodiments of the invention have beendescribed. For instance, an illumination device that includes lightguides illuminated by a light emitting diode in a manner that takesadvantage of radiation patterns having angularly displaced maximumluminous intensity have been described for use in any lighting system.Nevertheless, it is understood that various modifications can be madewithout departing from the spirit and scope of the invention. Forexample, the invention may be used in any application where lighting isdesirable, including such applications as functional or decorativelighting for buildings, water fountains, instrument panels of vehicles,aircrafts or watercrafts, Christmas tree decorations, isle lighting fortheaters or the like, neon-like light guide signs, turn-signals or brakelights on vehicles or any other application where lighting is desirable.Accordingly, other implementations and embodiments are within the scopeof the following claims.

1. A sign comprising: a frame; a light emitting diode housed within theframe; a first light guide positioned to be illuminated by the lightemitting diode, wherein the first light guide provides directional sidelighting in a first direction; and a second light guide positioned to beilluminated by the light emitting diode, wherein the second light guideprovides directional side lighting in a second direction.
 2. The sign ofclaim 1, wherein the frame is formed with holes and the each light guideprotrudes through at least one of the holes.
 3. The sign of claim 1,wherein the light emitting diode is a first light emitting diode, thesign further comprising a second light emitting diode housed within theframe, wherein the first and second light guides are positioned to beilluminated by the second light emitting diode.
 4. The sign of claim 1,wherein the first and second light guides provide lighting in differentcolors.
 5. The sign of claim 1, wherein the light emitting diode emits aradiation pattern, wherein a maximum luminous intensity of the radiationpattern is displaced relative to a center axis of the light emittingdiode.
 6. The sign of claim 5, wherein each of the first and secondlight guides is positioned to be illuminated by the light emitting diodeat offset locations relative to the center axis of the light emittingdiode.
 7. The sign of claim 6, wherein each of the first and secondlight guides is positioned such that a cross-sectional center of eachlight guide substantially corresponds to locations of the maximumluminous intensity of the radiation pattern of the light emitting diode.